On Tue, Oct 24, 2017 at 07:50:06PM +0530, Ravi Bangoria wrote:
> Perf top is often crashing at very random locations on powerpc.
> After investigating, I found the crash only happens when sample
> is of zero length symbol. Powerpc kernel has many such symbols
> which does not contain length details in vmlinux binary and thus
> start and end addresses of such symbols are same.
>
> Structure
>
> struct sym_hist {
> u64 nr_samples;
> u64 period;
> struct sym_hist_entry addr[0];
> };
>
> has last member 'addr[]' of size zero. 'addr[]' is an array of
> addresses that belongs to one symbol (function). If function
> consist of 100 instructions, 'addr' points to an array of 100
> 'struct sym_hist_entry' elements. For zero length symbol, it
> points to the *empty* array, i.e. no members in the array and
> thus offset 0 is also invalid for such array.
>
> static int __symbol__inc_addr_samples(...)
> {
> ...
> offset = addr - sym->start;
> h = annotation__histogram(notes, evidx);
> h->nr_samples++;
> h->addr[offset].nr_samples++;
> h->period += sample->period;
> h->addr[offset].period += sample->period;
> ...
> }
>
> Here, when 'addr' is same as 'sym->start', 'offset' becomes 0,
> which is valid for normal symbols but *invalid* for zero length
> symbols and thus updating h->addr[offset] causes memory corruption.
>
> Fix this by adding one dummy element for zero length symbols.
>
> Fixes: edee44be5919 ("perf annotate: Don't throw error for zero length
> symbols")
> Signed-off-by: Ravi Bangoria <ravi.bango...@linux.vnet.ibm.com>
Acked-by: Namhyung Kim <namhy...@kernel.org>
Thanks,
Namhyung
> ---
> tools/perf/util/annotate.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
> index 4397a8b..15db525 100644
> --- a/tools/perf/util/annotate.c
> +++ b/tools/perf/util/annotate.c
> @@ -606,9 +606,19 @@ static struct arch *arch__find(const char *name)
> int symbol__alloc_hist(struct symbol *sym)
> {
> struct annotation *notes = symbol__annotation(sym);
> - const size_t size = symbol__size(sym);
> + size_t size = symbol__size(sym);
> size_t sizeof_sym_hist;
>
> + /*
> + * Add buffer of one element for zero length symbol.
> + * When sample is taken from first instruction of
> + * zero length symbol, perf still resolves it and
> + * shows symbol name in perf report and allows to
> + * annotate it.
> + */
> + if (size == 0)
> + size = 1;
> +
> /* Check for overflow when calculating sizeof_sym_hist */
> if (size > (SIZE_MAX - sizeof(struct sym_hist)) / sizeof(struct
> sym_hist_entry))
> return -1;
> --
> 1.8.3.1
>
